Induction of multiple chromosome interchanges in pearl millet, Pennisetum typhoides.

With a view to building up a series of translocation stocks and also, eventually, a complex heterozygote involving all the 14 chromosomes of pearl millet, its seeds were exposed to gamma rays from a (60)Co Gamma Source. Seeds from the meiotically established interchanges were given several cycles of gamma irradiation. Frequency of the incidence of interchange heterozygotes in different generations was scored. As well as receiving recurrent irradiation, different translocation stocks were intercrossed to build up higher interchange configurations and also to identify the translocated chromosomes. Interchanges involving more than 12 of the 14 chromosomes were not obtained, presumably because the somatic and gametic sieves operate more rigorously when more chromosomes are involved in interchanges. It is nevertheless suggested that the karyomorphological features of pearl millet, including its symmetrical karyotype, are favourable for the induction, and also perhaps the maintenance, of translocation heterozygosity. Possible use of translocation heterozygotes in building aneuploids and certain duplications of value in breeding is suggested.